The present invention relates to a carboxyl-containing alicyclic compound as a useful monomer for preparing a photoresist resin and a process for preparing the same. More specifically, the present invention relates to a carboxyl-containing alicyclic compound which is useful as a monomer for synthesizing a photoresist resin for an E-beam (electron-beam), KrF, ArF, an X-ray or EUV which can be applied to a high-density micro-pattern of not more than 0.15 xcexcm (DRAM of 1 G or more).
Most of the conventional ArF photoresist resins have low-etching resistance and insufficient resolution. Physical properties of a photoresist resin are affected by the type of monomers used for preparing the resin, and the production cost of a photoresist resin is very high because of the high price of the monomers used for the resin, so that mass production of the photoresist resin has been restricted. Thus, a lot of attempts have been made to develop the most proper monomer for economically producing a photoresist resin having excellent resolution and etching resistance on a large scale.
The object of the present invention is to provide photoresist monomers and copolymers which are appropriate for a lithography process using a light source having a short wavelength of not more than 250 nm.
The present invention also provides photoresist compositions comprising said copolymers.
Furthermore, the present invention provides a process for forming a photoresist pattern by using said photoresist composition and a process for preparing a semiconductor element therefrom.
Now, the present Invention is described in more detail.
The present inventors have discovered the surprising fact that the alicyclic compounds represented by Chemical Formula 1 below, which have one or more carboxylic groups or tert-butyl groups, are useful as a monomer employed in the synthesis of a photoresist resin for an ArF, EUV, E-beam or X-ray light source. The compounds of the present invention have high purity and low price, so that a photoresist resin of high performance can be economically produced on a large scale therefrom.
[Chemical Formula 1]
In the above formula, R1 and R2, which may be identical to or different from each other, represent hydrogen or a tert-butyl group; X represents hydrogen, hydroxy or oxygen; and n represents a number from 1 to 3.
Furthermore, the present inventors have found that an excellent pattern can be obtained in a lithography process employing a light source of an extremely short wavelength, by using a photoresist composition comprising the compound represented by Chemical Formula 1.
Among the carboxyl-containing alicyclic compounds of the present invention represented by Chemical Formula 1, preferred compounds are listed below:
(a) Compounds of the following formula wherein R1 and R2 individually represent tert-butyl and X represents oxygen, such as 5-norbornene-2-carbonyl di-tert-butyl malonate; bicyclo[2,2,2]oct-5-ene-2-carbonyl di-tert-butyl malonate; or bicyclo[3,2,2]non-8-ene-2-carbonyl di-tert-butyl malonate:
[Formula 1a]
(b) Compounds of the following formula wherein R1 is tert-butyl, R2 is hydrogen and X is oxygen, such as 5-norbornene-2-carbonyl mono-tert-butyl malonate; bicyclo[2,2,2]oct-5-ene-2-carbonyl mono-tert-butyl malonate; or bicyclo[3,2,2]non-8-ene-2-carbonyl mono-tert-butyl malonate:
[Formula 1b]
(c) Compounds of the following formula wherein R1 and R2 individually represent hydrogen and X represents oxygen, such as 5-norbornene-2-carbonyl malonic acid; bicyclo[2,2,2]oct-5-ene-2-carbonyl malonic acid; or bicyclo[3,2,2]non-8-ene-2-carbonyl malonic acid:
[Formula 1c]
(d) Compounds of the following formula wherein R1 and R2 individually represent tert-butyl and X represents the hydroxy group, such as 5-norbornene-2-yl di-tert-butylhydroxymethyl malonate; bicyclo[2,2,2]oct-5-ene-2-yl di-tert-butylhydroxymethyl malonate; or bicyclo[3,2,2]non-8-ene-2-yl di-tert-butylhydroxymethyl malonate:
[Formula 1d]
(e) Compounds of the following formula wherein R1 is tert-butyl, R2 is hydrogen and X is a hydroxy group, such as 5-norbornene-2-yl mono-tert-butylhydroxymethyl malonate; bicyclo[2,2,2]oct-5-ene-2-yl mono-tert-butylhydroxymethyl malonate; or bicyclo[3,2,2]non-8-ene-2-yl mono-tert-butylhydroxymethyl malonate:
[Formula 1e]
(f) Compounds of the following formula wherein R1 and R2 individually represent hydrogen and X represents a hydroxy group, such as 5-norbornene-2-yl hydroxymethylmalonic acid; bicyclo[2,2,2]oct-5-ene-2-yl hydroxymethylmalonic acid; or bicyclo[3,2,2]non-8-ene-2-yl hydroxymethylmalonic acid:
[Formula 1f]
(g) Compounds of the following formula wherein R1 and R2 individually represent tert-butyl and X represents hydrogen, such as 5-norbornene-2-yl di-tert-butylmethyl malonate; bicyclo[2,2,2]oct-5-ene-2-yl di-tert-butylmethyl malonate; or bicyclo[3,2,2]non-8-ene-2-yl di-tert-butylmethyl malonate:
[Formula 1g]
(h) Compounds of the following formula wherein R1 is tert-butyl, R2 is hydrogen and X is hydrogen, such as 5-norbornene-2-yl mono-tert-butylmethyl malonate; bicyclo[2,2,2]oct-5-ene-2-yl mono-tert-butylmethyl malonate; or bicyclo[3,2,2]non-8-ene-2-yl mono-tert-butylmethyl malonate:
[Formula 1h]
(i) Compounds of the following formula wherein R1, R2 and X individually represent hydrogen, such as 5-norbornene-2-yl methylmalonic acid; bicyclo[2,2,2]oct-5-ene-2-yl methylmalonic acid; or bicyclo[3,2,2]non-8-ene-2-yl methyl malonic acid.
[Formula 1i]
The carboxyl-containing alicyclic compound of the present invention, represented by Chemical Formula 1, can be prepared by reacting a compound represented by Chemical Formula 2 below with a malonate represented by Chemical Formula 3:
R4O2Cxe2x80x94Cxe2x8ax96HNaxe2x8ax96xe2x80x94CO2R5
in the presence of a solvent such as tetrahydrofuran (THF), dimethylformamide (DMF) or dioxane.
[Chemical Formula 2]
In Formula 2 above, R3 represents hydrogen, or halogen such as chloro, bromo and iodo, Y represents hydrogen or oxygen, n is a number from 1 to 3, and R4 and R5, which may be identical to or different from each other, represent the tert-butyl group or a sodium ion.
The compound represented by Chemical Formula 2, which is used as a starting material in the present invention can be prepared as follows:
The alicyclic compound of Chemical Formula 2 wherein R3 is hydrogen or halogen and Y is oxygen, is prepared by reacting 1,3-cyclopentadiene, 1,3-cyclohexadiene or 1,3-cycloheptadiene with acroyl halide or acrolein at a temperature between xe2x88x9240xc2x0 C. to 80xc2x0 C., preferably between xe2x88x9220xc2x0 C. to 30xc2x0 C. in an equivalent ratio of 1:1, as shown in the following Reaction Scheme A:
[Reaction Scheme A]
The alicyclic compound of Chemical Formula 2 wherein R3 is a halogen such as bromo, chloro or iodo and Y is hydrogen, is prepared by reacting 5-norbornene-2-methanol, [2,2,2]bicyclooctene-2-methanol or [3,2,2]bicyclononene-6-methanol with some excess of thionyl chloride (1.2 equiv.) at a temperature between xe2x88x9240xc2x0 C. to 80xc2x0 C., preferably between 0xc2x0 C. to 25xc2x0 C., as shown in the following reaction scheme B:
[Reaction Scheme B]
The malonic acid compounds of the present invention, represented by Chemical Formula 3, include:
sodium salt of di-tert-butyl malonate;
(CH3)3CO2Cxe2x80x94Cxe2x8ax96HNa⊕xe2x80x94CO2C(CH3)3
sodium salt of mono-tert-butyl malonate;
Na⊕xe2x8ax96O2Cxe2x80x94Cxe2x8ax96HNa⊕xe2x80x94CO2C(CH3)3
sodium malonate;
Na⊕xe2x8ax96O2Cxe2x80x94Cxe2x8ax96HNa⊕xe2x80x94CO2xe2x8ax96Na⊕
In the process according to the present invention, the compound of Chemical Formula 2 and malonate salt of Chemical Formula 3 are preferably reacted in a molar ratio of 1:1. As a reaction solvent, tetrahydrofuran (THF), dimethylformamide (DMF), dioxane, or the like is used, and the amount of the solvent is preferably in a 5 to 50 weight ratio to the compound of Chemical Formula 2.
Synthesis of a Photoresist Copolymer
A photoresist polymer according to the present invention can be obtained by copolymerizing a photoresist monomer of the present invention with one or more compound(s) represented by Chemical Formula 4:
[Chemical Formula 4]
wherein, i represents a number from 1 to 3 , m and n independently represent a number from 1 to 3, and R6 and R7 independently represent an alkyl group or a cyclic alkyl group having 0 to 10 carbon atoms.
The copolymer resin (Chemical Formulas 4-7) of the present invention can be prepared according to conventional techniques such as bulk polymerization, solution polymerization, or the like. Polymerization initiators which can be used in the present invention include benzoyl peroxide, 2,2xe2x80x2-azobisisobutyronitrile (AIBN), acetyl peroxide, lauryl peroxide, tert-butyl peracetate, di-tert-butyl peroxide, and the like. As a solvent, cyclohexanone, methyl ethyl ketone, benzene, toluene, dioxane, dimethylformamide may be used individually or as a mixed solvent.
As to the polymerization conditions used in preparing the copolymer resin according to the present invention, conventional radical polymerization temperatures and pressures may be adjusted depending on the properties of the reactants, but polymerization is preferably carried out at a temperature between 60xc2x0 C.-200xc2x0 C. In a nitrogen or an argon atmosphere for 4-24 hours.
Preferable photoresist copolymers according to the present invention include the compound represented by the following Chemical Formula 5:
[Chemical Formula 5]
wherein, i and k independently represent numbers from 1 to 3, c is 1 or 2, m and n independently represent a number from 1 to 3, R6 and R7 independently represent an alkyl group or a cyclic alkyl croup having 0 to 10 carbon atoms, and a, b, c and d individually represent polymerization ratios of each comonomer, preferably, a=5-20 mol %, b=50 mol %, c=0-30 mol % and d=5-20 mol %.
As a solvent for purifying the copolymer by crystallization, alcohols (methanol, ethanol, isopropanol) or petroleum ether may be used instead of diethyl ether.
[Chemical Formula 6]
The copolymer resin according to the present invention can be used in forming a positive micro-image by mixing a conventional inorganic photoacid generator in an organic solvent according to a conventional process for preparing a photoresist solution. In the process of forming a photosensitive film pattern on a semiconductor element, the amount of the copolymer resin of the present invention can be varied depending upon the type of organic solvent or inorganic photoacid generator used, or the lithography conditions. However, about 10-30 wt % of the copolymer based on the organic solvent used in preparing the photoresist is generally used.
Now, the process for forming a photosensitive film pattern of a semiconductor element by using the copolymer of the present invention is described in more detail.
A copolymer of the present invention is dissolved in cyclohexanone to provide a concentration of 10-13% by weight, and an onium salt or organic sulfonic acid as an inorganic photoacid generator is incorporated thereto in a concentration of 0.1-10% by weight, and the solution is filtered with an ultra-micro filter to prepare a photoresist solution. Usable inorganic photoacid generators include triphenylsulfonium triplate, dibutylnaphthylsulfonium triplate, 2,6-dimethylphenylsulfonate, bis(arylsulfonyl)-diazomethane, oxime sulfonate and 2,1-diazonaphthoquinon-4-sulfonate.
As an organic solvent, ethyl 3-ethoxypropionate, methyl 3-methoxypropionate, propyleneglycol methyl ether acetate, or the like may be used instead of cyclohexanone. The amount of the solvent is preferably 200 to 1000% by weight based on the amount of the photoresist resin used.
The photoresist solution thus prepared is spin-coated on a silicon wafer to prepare a thin film, and the wafer is preheated in an oven or a hot plate at 80xc2x0-150xc2x0 C. for 1-5 minutes, exposed to light by using a far ultraviolet light exposer device or excimer laser exposer device, and then post-heated at a temperature between 100xc2x0-200xc2x0 C. for 1 second to 5 minutes. The resulting, exposed wafer is impregnated in 2.38% aqueous TMAH solution for 1-1.5 minutes to obtain a positive resist pattern.
ArF, KrF, an E-beam, EUV (extreme ultraviolet) or an ion beam may also be used as a light exposer. The energy of the light exposure is preferably 0.1-10 Mj/cm2.
Now, the present invention is described in more detail by referring to the Examples. However, it should not be understood that the technical scope of the present invention is restricted to these Examples by any means.